About Hybrid-graphics Technologies

The laptop manufacturers developed new technologies involving two graphic cards in an single computer, enabling both high performance and power saving usages. This technology is well supported on Windows but it's still quite experimental with Linux distributions.

We call hybrid graphics a set of two graphic cards with different abilities and power consumptions. There are a variety of technologies and each manufacturer developed its own solution to this problem. Here we try to explain a little about each approach and models and some community solutions to the lack of GNU/Linux systems support.

The "Old" Hybrid Model (Basic Switching)

This approach involves a two graphic card setup with a hardware multiplexer (MUX). It allows power save and low-end 3D rendering by using an Integrated Graphics Processor (IGP); or a major power consumption with 3D rendering performance using a Dedicated Graphics Processor (DGP). This model makes the user choose (at boot time or at login time) within the two power/graphics profiles and is almost fixed through all the user session. The switch is done by a similar workflow:

Turn off the display

Turn on the DGP

Switch the multiplexer

Turn off the IGP

Turn on again the display

This switch is somewhat rough and adds some blinks and black screens in laptops that could do it "on the fly". Later approaches made the transition a little more user-friendly.

The New Dynamic Switching Model

Most of the new Hybrid-graphics technologies involves two graphic cards as the basic switching but now the DGP and IGP are plugged to a framebuffer and there is no hardware multiplexer. The IGP is always on and the DGP is switched on/off when there is a need in power-save or performance-rendering. In most cases there is no way to use only the DGP and all the switching and rendering is controlled by software.
At startup, the Linux kernel starts using a video mode and setting up low-level graphic drivers which will be used by the applications. Most of the Linux distributions then use X.org to create a graphical environment. Finally, a few other softwares are launched, first a login manager and then a window manager, and so on. This hierarchical system has been designed to be used in most of cases on a single graphic card.

See the "works"? This means the script found a bus which your GPU sits on and it has now turned off the chip. To confirm this, your battery time remaining should have increased. Currently, the chip will turn back on with the next reboot to get around this we do the following:

Note: To turn the GPU back on just reboot.

Add the kernel module to the array of modules to load at boot:

/etc/modules-load.d/acpi_call.conf

#Load 'acpi_call.ko' at boot.
acpi_call

To turn off the GPU at boot we could just run the above script but honestly that is not very elegant so instead lets make use of systemd's tmpfiles.

/etc/tmpfiles.d/acpi_call.conf

w /proc/acpi/call - - - - \_SB.PCI0.PEG0.PEGP._OFF

The above config will be loaded at boot by systemd. What it does is write the specific OFF signal to the /proc/acpi/call file. Obviously, replace the \_SB.PCI0.PEG0.PEGP._OFF with the one which works on your system.

Note: After every kernel upgrade acpi_call-git will need to be reinstalled.